1. Field of the Invention
This invention relates to a cartridge-needle unit having a needle that can retract within the cartridge after use for safe disposal and to a safety syringe comprising such cartridge-needle unit.
2. Description of the Prior Art
Disposable medicament-containing cartridge needle units for use in conjunction with reusable hypodermic syringe holders are well known in the art and in widespread commercial use. Such cartridges conventionally feature a cylindrical body closed at the proximal end with a flexible plunger slidable within the bore of the cartridge and closed at the distal necked-down end with a septum secured to the cartridge by a crimped-on aluminum collar. The necked-down distal end conventionally is fitted with a needle hub/needle/needle sheath assembly. Such cartridge-needle units are available from Sanofi Winthrop Pharmaceuticals under the Carpuject.RTM. trademark.
In use, the cartridge-needle unit must be activated, i.e., the proximal end of the needle cannula must penetrate the sealed septum such that communication is achieved between the fluid and the proximal end of the needle. Some cartridge-needle units are sold in an activated form. Others must be activated by the user. When user activated cartridge-needle units are used in conjunction with conventional reusable syringe holders of the type described, for example, in Hadtke, U.S. Pat. No. 4,585,445 and in EP-A 485,028, this is accomplished when the health care worker advances the cartridge through the holder by rotating a clamping element.
Many holders, including the above-referenced reusable holders, enable the user to avoid handling the cartridge-needle unit when the needle unit is exposed. Nevertheless, health care workers are especially susceptible to accidental and potentially infectious, and indeed, on occasion, possibly fatal, needle strikes due to the careless handling and/or disposing of the cartridge-needle unit after use. The consequences to health care workers of strikes from needles contaminated with various infectious diseases such as hepatitis or AIDS can be particularly severe. The frequency of accidental needle strikes in the United States is surprisingly great, and has been estimated to be approximately one million strikes per year. Moreover, the cost to health care organizations for the testing of health care workers accidentally stricken by used needles is a significant burden on health care costs. This is illustrated in a recent report by Kirkland, Safer Syringes Boost Molder Opportunities, Plastics World, August 1993, pp. 20-24, which states:
"The average cost associated with accidental needle-stick injury in the U.S. reportedly is $3 billion/year. For example, estimates for the average cost associated with testing alone is at least $1,200 per injury. This does not take into account the cost of treatment if disease develops (estimated at $15,700), litigation costs, increased insurance premium costs, replacement of the injured worker, OSHA fines and other costs."
Therefore, it would be desirable to further protect health care workers by providing systems which reduce the possibility of accidental needle strikes.
To this end, it has been suggested to provide syringes having a retractable needle. For example, Haber et al, U.S. Pat. No. 4,909,794, describe a combination retractable needle cannula and cannula lock for a medication carpule, i.e., cartridge. The cannula lock includes a clamp having a pair of jaws which are normally separated from one another so that the needle can be releasably retained therebetween. In the pre-injection state, the clamp is axially spaced from the cartridge, and the jaws of the clamp are rotated towards one another to retain the cannula in an axially extended position for administering an injection. Post-injection, the health care worker continues to apply pressure to the piston stem forcing the empty cartridge to move forward such that the needle embeds in the plunger. Further movement displaces the clamp, whereby the jaws of the clamp rotate away from one another to release the cannula. The cannula may then be retracted within and completely surrounded by the empty cartridge so that the cannula can be safely discarded.
However, the system proposed in U.S. Pat. No. 4,909,794 has been found to be less than satisfactory from a commercial standpoint for a variety of reasons, resulting from both inherent design limitations and reliability concerns.
First, because the needle is released from the jaws of the clamp by the health care worker continuing to apply an axially and distally directed force beyond the point at which all medication is delivered, there is an unacceptably high probability that the health care worker may prematurely release the needle while it is still embedded in the patient. One possible consequence of this may be that the health care worker must then remove a lone sharp needle from the patient.
Second, unlike most current commercial hypodermic syringe designs, this prior art system relies upon an interference fit between the jaws and the hub in order to wedge the needle in place. In fact, Haber et al suggest that the proximal surface of the cannula be textured to enhance the frictional retention of the needle. However, if the frictional force is not great enough, the needle may slip with respect to the jaw both upon injection and removal from the patient. If the fit is too tight and the frictional force is too high, the user may have to deliver an unreasonably high force to release the jaw from the hub. More generally, friction is an unreliable force to use for such a critical function, inasmuch as small variations in dimension, surface finish, cleanliness, or even temperature can alter the desired retention force. While some modifications can be made to improve the reliability of this device and its use of friction, ultimately, there are limitations.
Third, after the jaw is released from the hub, the needle is freed to be withdrawn into the cartridge by the plunger. However, any body fluid and/or medication that may remain on the tip of the needle after removal from the patient can be wiped on the jaw as the needle is retracted. This body fluid then remains in an unprotected area and presents some level of danger to the health care worker.
Haber, U.S. Pat. No. 4,935,014, which is a continuation-in-part of the above-described Haber et al patent, describes another combination retractable needle cannula and cannula lock embodiment in which the jaws of the clamp in the pre-injection state are surrounded by and rotated towards one another by an expandable outer sleeve which retains the cannula in an axially extended position between the jaws for administering an injection. Post-injection, the clamp is displaced outwardly of the sleeve, whereby the jaws are free to release the cannula. It appears that the sleeve enables the syringe to be adapted for use with a cartridge having a head which is narrower in diameter than the cylindrical body. In any event, the syringe described by Haber in U.S. Pat. No. 4,935,014 contains jaws and suffers from the same inherent design limitations and reliability concerns as described above.
It would be desirable to provide a cartridge-needle unit having a retractable needle which (1) reduces the tendency for body fluids and/or medication to remain in an unprotected area upon retraction of the needle into the cartridge, (2) does not rely upon an unpredictable frictional fit between the needle and hub and (3) virtually eliminates the possibility that the needle can be released into the patient.